ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

sans partage d'une aire ou les vestiges de la basse surface
52 se tiennent en contrebas des temoins d'un aplanissement
plus ancien, 51.
L'analyse du dispositif etage culminant 51 - 52 dans les
Monts du Haut-Dourdou (serie sedimentaire plissee et faillee
cambro-silurienne) corrobore en outre un enseignement
fondamental tire de l'examen des faits d' etagernent
des deux surfaces d'aplanissements dans les.Monts de Lacaune
(granites et gneiss de metamorphic core complex): a
savoir que la haute et la basse surface sont non pas des niveaux
d' altitude qui tireraient leur justification de pures
concordances altimetriques, mais des aplanissements cycliquement
etages, autrement dit d' anciennes formes fonctionnelles.
Ces deux surfaces ont ainsi enregistre, au cours
de leur tres longue histoire, les effets de diverses deformations
tectoniques. Si les unes (ante-52) n' ont interesse que
la surface S1' les autres (post-Sy) ont par contre affecte en
bloc S1 et S2' D'ou. la circonspection avec laquelle il convient
d'utiliser ici le ternoignage des modeles numeriques
de terrain, les deux aplanissements etages etant des surfaces
gauches et non plus des surfaces subhorizontales.
THOMAS GLADE
Spatial and temporal occurrence of rainfall-triggered
landslides in New Zealand
Research School of Earth Science, Department of Geography,
Victoria University of Wellington, p.o. box 600, Wellington, New Zealand
Rainfall-triggered landslide events are a common problem
in New Zealand and some have caused extensive damage.
Many of these events have been investigated on a regional
or site level by various institutions, such as: universities,
territorial and regional authorities, Crown Research Institutes,
private consultancies, and transport authorities. The
output from these investigations is strongly dependent on
their specific aims. These studies use different methodologies
and techniques related to the nature of the individual
problem being investigated, which makes comparative
analysis difficult. However, these investigations demonstrate
the widespread influence of landslides on all aspects of
life and environment and illustrate the need for further detailed
investigation.
On the regional scale, studies relating landslide occurrence
to rainfall distribution in space and time are rare, which is
surprising because of the high yearly total damage caused
by rainfall-triggered landslides in New Zealand. The knowledge
of rainfall/landslide relationship has potential value
to farmers, land managers, politicians, engineers, territorial
and regional officials, transport authorities, and insurance
companies. Historical records indicate that most parts of
the country can expect to suffer damage from this phenomenon.
Other overseas agencies have already responded to
this need. For example, the U.S. Geological Survey established
a real time landslide warning system during heavy
rainfalls in the San Francisco Bay Region, California, USA,
which operated successfully during a rainstorm in February
1986.
For this investigation, three different regions within the
North Island of New Zealand have been chosen to compare
magnitude and frequency relationship between landslides
and rainfall in both time and space. The regions are
Northern Hawke's Bay, Wairarapa, and Wellington. They
were selected because of the availability of the necessary
temporal and spatial rainfall data, a good landslide record,
differences in their physical environment and a complete
aerial photo coverage for these areas, especially after highly
damaging landslide events.
The study aims are:
1. establishing regional rainfall thresholds, their probabilities
of occurrence as well as the probabilities that rainfall
of a given magnitude and frequency trigger landslides, by
comparing historical records of landslide occurrence with
time series rainfall data,
2. relating these thresholds to antecedent soil water conditions,
3. analysing for one episode per region the spatial extent
of landslide occurrence and its relationship to the distribution
of the triggering rainstorm,
4. summarising and characterising the similarities and/or
differences between these regions,
5. establishing a landslide hazard assessment for each region
on the basis on historical records.
The overall intention is to establish regional thresholds and
to develop some ideas of how rainfall cells trigger landslides
and which factors prepare and control the pattern and
nature of occurrence. Furthermore, these scientific results
are applied to the specific region by a landslide hazard assessment.
ANDREW I.W. GLEADOW 1 ,2 & RODERICK W. BROWN 2
Fission track thermochronology,
denudation and tectonics
1Australian Geodynamics Cooperative Research Centre
2 Vieps School of Earth Sciences, La Trobe University,
Bundoora, Victoria 3083, Australia
Thermochronology, the quantitative study of the thermal
histories of rocks through the use of temperature-sensitive
radiometric dating methods, provides a powerful new approach
to the quantitative reconstruction of long-term patterns
of denudation. Methods of quantitative thermal history
analysis are now largely based on the 40Ar/ 39 Ar and
fission track dating methods. Most of these mineral dating
systems are affected by temperatures that are typically
found at middle crustal depths, but one of them, the apatite
fission track system, is particularly useful for studies of
the low-temperature environments that prevail in the upper
several kilometres in the continental crust. Apatite is a
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